A power takeoff (PTO) unit may be used to transfer power between a prime mover, such as a diesel engine, and one or more hydraulic pumps. In applications where two or more hydraulic pump are in use, the total torque of the combined hydraulic pumps may, especially during transient conditions, exceed the torque rating of the PTO and/or the prime mover. Catastrophic failure of the prime mover may result.
An example is a road compactor that uses one hydraulic pump to drive a steering circuit and another hydraulic pump to drive a compactor unit. The startup of the compactor unit can cause very high transient pressures in the hydraulic circuit of the compactor hydraulic pump. If this occurs when a steering maneuver is in process, such as turning over a bump, the resulting total pressure demands in the respective hydraulic circuits can, in turn, create very high torques at the hydraulic pumps. The combined torque reflected back through the PTO to the prime mover can cause mechanical failures in critical components of a gear train of the PTO or the prime mover.
U.S. Published Patent Application 20070079533 (the '533 application) discloses a hydraulic system that uses a sensor on a hydraulic circuit with a compactor in a machine used for snow surface preparation. A sensor in the hydraulic circuit opens a shunt valve to bypass the compactor when the pressure in the hydraulic circuit exceed a pre-programmed pressure value. The '533 application fails to teach measuring the total pressure in multiple hydraulic circuits to determine when pressure should be reduced in only one of the multiple hydraulic circuits.